A giant sloth, a source of ornaments for prehistoric Brazilians

2023-07-13 19:35:49

The rock shelter of Santa Elina, in Mato Grosso, offers a wonderful summary of human occupation in Brazil. Apart from the very rich multi-secular figurative cave paintings, it has given archaeologists less visible clues to a much older presence of our species in these regions, in the form of bones and stone tools. But also intriguing “pearls” drawn from giant sloths, animals long extinct. A study published on July 12 in the Proceedings of the Royal Society B thus presents the analysis of three pierced osteoderms found in the oldest layers of the site, dated from 25,000 to 27,000 years ago.

Osteoderms of giant sloths having been perforated for use as adornment, found in the rock shelter of Santa Elina (Brazil), in levels dated more than 25,000 years ago. PANSANI ET AL., PRSB

Osteoderm? This term designates “small bony balls present in the skin of certain giant sloths, perhaps a vestige of their armored ancestors”, explains François Pujos. This paleontologist at the Argentine National Council for Scientific and Technical Research (Conicet), an organization comparable to the French National Center for Scientific Research (CNRS), was not involved in the Santa Elina study, but he is a specialist in Glossotherium phoenesisthe species of giant sloths found there. “These ossifications inside the dermis could function as an integrated armor”, he describes. They were vascularized, which suggests that they could also play a role in the thermal regulation of this family of animals, the largest of which could reach several tons – they were part of the “megafauna”, a group of mammals of great size, the last of which disappeared 11,000 to 12,000 years ago in America.

“At Santa Elina, more than 4,000 osteoderms were found spread over an area of ​​15 m2 of excavations”declares Agueda Vialou (National Museum of Natural History of Paris, Federal University of Bahia), who directed these from 1984 to 2005. They unearthed two specimens of Glossotherium, one in a layer dated to 12,000 years old, and the other in the oldest stratum, over 25,000 years old. It is in this that three osteoderms have attracted the attention of archaeologists, due to perforations which they have attributed to humans – Agueda and her husband, Denis Vialou, estimating from the end of the 1990s that they could have been used as adornment or pendant.

The new study aimed to remove doubts about the intentional origin of these perforations, thanks to use-wear work using several imaging techniques. “We wanted to be as certain as possible that they could not result from physico-chemical processes and animal interventions”, specifies Loïc Bertrand, chemist of ancient materials and director of research at the Ecole Normale Supérieure Paris-Saclay. The pieces therefore came from Brazil to be subjected to X-rays from the European Synchrotron Radiation Facility in Grenoble and to photoluminescence analyzes to assess the contemporaneity of the perforations and polishing observed on the osteoderms. They have also been compared to experimentally modified fossil osteoderms.

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